THIS AVALANCHE FORECAST EXPIRED ON April 23, 2018 @ 6:32 am
Avalanche Forecast published on April 22, 2018 @ 6:32 am
Issued by Brandon Schwartz - Tahoe National Forest

Areas of MODERATE avalanche danger will exist today at all elevations. A loose wet avalanche problem will develop quickly this morning in areas where a poor snow surface refreeze occurred last night. Avoid travel in or below avalanche terrain on slopes with marginally supportable to unsupportable wet snow conditions or on slopes where roller balls are occurring. This is the last avalanche advisory of the 2017/2018 season.

2. Moderate

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Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Loose Wet
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Air temperatures were warm last night, generally in the 40s for most mid and upper elevation locations. A thin superficial refreeze will likely have occurred overnight on open slopes due radiational cooling under clear skies. Below treeline, the snow surface may not have refrozen at all last night under areas of dense forest canopy. The Carson Pass area was colder last night and may have had a bit better of a refreeze. Regardless of if overnight refreeze was poor or decent, rapid warming today will allow for a loose wet avalanche problem to develop quickly on all aspects at all elevations. Avalanche size up to D2 is possible (large enough to bury or injure a person).

Monitor snow surface conditions as the day progresses. Pay attention to supportability of melt-freeze crust at the snow surface. Pick an area not compacted by previous tracks and punch a hole in the crust to gauge crust thickness. Compare surface crust thickness on open slopes to areas under dense forest canopy in order to get a sense of the overall strength of refreeze in the area. Once melt makes the surface crust marginally supportable to unsupportable, loose wet avalanches are possible. Human triggered roller balls are also a sign of potentially unstable snow. Avoid travel in or below avalanche terrain on slopes with marginally supportable to unsupportable wet snow conditions or on slopes where roller balls are occurring.

recent observations
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* Observations were made and received yesterday from Andesite Peak and Castle Peak (Donner Summit area). A weak overnight snow surface refreeze had occurred in the area with signs of loose wet instability present on E and NE aspects at 9:15 am.

* Snow cover continues to become thin to nonexistent in the lower elevations of the forecast area. Snow cover improves above 7,200'-8,000' depending on location. Numerous open creeks exist below 8,000'.

Weather and CURRENT CONDITIONS
weather summary

A weather disturbance will pass by today to the north of the forecast area. This will mostly increase SW winds this afternoon and produce some cumulus cloud build ups. Thunderstorms are unlikely, but cannot be ruled out entirely this afternoon over the Sierra Crest. Air temperature inversion conditions are in place this morning with the coldest air on the mountain valley floors and air temperatures in the 40s for most mid and upper elevation locations. Maximum daytime air temperatures will once again reach 10 to 15 degrees above average today. Similar warm air temperatures with light wind is forecast for Monday.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 41 to 47 deg. F.
Max. temperature: 56 to 60 deg. F.
Average ridgetop wind direction: NE shifting to SW
Average ridgetop wind speed: NE 17 mph | SW 15 mph
Maximum ridgetop wind gust: NE 21 mph | SW 30 mph
New snowfall: 0 inches
Total snow depth: 46 to 90 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Sunday Sunday Night Monday
Weather: Sunny skies, becoming partly cloudy. Clear skies. Sunny skies, becoming partly cloudy.
Temperatures: 57 to 63 deg. F. 30 to 35 deg. F. 57 to 63 deg. F.
Mid Slope Winds: SW W Variable
Wind Speed: Light winds increasing to 10 to 15 mph in the afternoon. Gusts up to 30 mph. 10 to 15 mph with gusts to 30 mph in the evening, becoming light. Light winds
Expected snowfall: 0 0 0
For 8000 ft. to 9000 ft.
Sunday Sunday Night Monday
Weather: Sunny skies, becoming partly cloudy. Clear skies. Sunny skies, becoming partly cloudy.
Temperatures: 51 to 57 deg. F. 30 to 35 deg. F. 50 to 58 deg. F.
Ridge Top Winds: SW W Variable
Wind Speed: 15 to 20 mph. Gusts to 25 mph increasing to 35 mph in the afternoon. 10 to 15 mph with gusts to 35 mph in the evening, becoming light. Light winds
Expected snowfall: 0 0 0
Disclaimer

This avalanche advisory is provided through a partnership between the Tahoe National Forest and the Sierra Avalanche Center. This advisory covers the Central Sierra Nevada Mountains between Yuba Pass on the north and Ebbetts Pass on the south. Click here for a map of the forecast area. This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.

For a recorded version of the Avalanche Advisory call (530) 587-3558 x258